Low glass transition temperature polymer latex drag reducing agent

ABSTRACT

Implementations described herein generally relate to a drag reducing agent (DRA) for improving flow of crude oils having high asphaltene content through pipelines. The DRA is a terpolymer having a glass transition temperature (T g ) of 6 degrees Celsius or below. The terpolymer is formed by a first monomer, a second monomer, and a third monomer. The first and second monomers are chosen based on the glass transition temperatures of corresponding homopolymers. The glass transition temperature of the homopolymer formed with the first monomer is at least 120 degrees Celsius higher than the glass transition temperature of the homopolymer formed with the second monomer. The DRA comprised of the terpolymer formed with the second monomer produces softer solids and fewer solids due to the low glass transition temperature of the terpolymer. The softer solids are more easily handled by the pump to keep the injection system clear.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/632,089, filed on Feb. 19, 2018, which is incorporatedherein by reference.

BACKGROUND Field

Implementations described herein generally relate to drag reducingagents for improving flow of crude oils having high asphaltene contentthrough pipelines.

Description of the Related Art

The flow of liquid in a conduit, such as a pipeline, typically resultsin frictional energy losses. Due to this energy loss, the pressure ofthe liquid in the conduit decreases along the conduit in the directionof the flow. For a conduit of fixed diameter, this pressure dropincreases with increasing flow rate. When the flow in the conduit isturbulent (e.g., Reynold's number greater than about 2100), certainultrahigh molecular weight polymers can be added to the liquid flowingthrough the conduit to reduce the frictional energy losses and alter therelationship between pressure drop and flow rate. These polymers aresometimes referred to as drag reducing agents (“DRAs”), and theyinteract with the turbulent flow processes and reduce frictionalpressure losses such that the pressure drop for a given flow rate isless, or the flow rate for a given pressure drop is greater. BecauseDRAs reduce frictional energy losses, increase in the flow capability ofpipelines, hoses and other conduits in which liquids flow is possible.DRAs can also decrease the cost of pumping fluids, the cost of equipmentused to pump fluids, and provide for the use of a smaller pipe diameterfor a given flow capacity. Accordingly, an ongoing need exists to formimproved drag reducing materials.

It has been identified that certain polymers, such as copolymers, havegood affinity for crude oils having high asphaltene contents (threeweight percent or more), and these polymers are effective DRAs inasphaltenic crude oils. However, these polymers form hard, brittlesolids when pumped into the pipeline, leading to plugged downstreamequipment.

Therefore, an improved DRA for crude oils having high asphaltene contentis needed.

SUMMARY

Implementations described herein generally relate to drag reducingagents for improving flow of crude oils having high asphaltene contentthrough pipelines. In one implementation, a composition for improvingflow of crude oils having asphaltene contents of three percent of higherin pipelines, the composition including a terpolymer having a glasstransition temperature of six degrees Celsius or below, and a continuousphase.

In another implementation, a drag reducing agent including a terpolymerformed by a first monomer, a second monomer, and a third monomer,wherein the first monomer is capable of forming a homopolymer having afirst glass transition temperature, the second monomer is capable offorming a homopolymer having a second glass transition temperature,wherein the second glass transition temperature is at least 120 degreesCelsius lower than the first glass transition temperature.

In another implementation, a drag reducing agent including a terpolymerincluding a terpolymer comprising five to 45 mole percent of a firstmonomer, 10 to 70 mole percent of a second monomer, and 10 to 80 molepercent of a third monomer, wherein the first monomer is selected fromthe group consisting of styrene, 4-methylstyrene, 4-(tert-butyl)styrene, benzyl methacrylate, phenyl methacrylate, and methylmethacrylate, the second monomer is selected from the group consistingof 2-ethylhexyl acrylate, n-butyl acrylate, and isodecyl acrylate.

DETAILED DESCRIPTION

Implementations described herein generally relate to a drag reducingagent (DRA) for improving flow of crude oils having high asphaltenecontent through pipelines. The DRA is a terpolymer having a glasstransition temperature (T_(g)) of 6 degrees Celsius or below. Theterpolymer is formed by a first monomer, a second monomer, and a thirdmonomer. The first and second monomers are chosen based on the glasstransition temperatures of corresponding homopolymers. The glasstransition temperature of the homopolymer formed with the first monomeris at least 120 degrees Celsius higher than the glass transitiontemperature of the homopolymer formed with the second monomer. The DRAcomprised of the terpolymer formed with the second monomer producessofter solids and fewer solids due to the low glass transitiontemperature of the terpolymer. The softer solids are more easily handledby the pump to keep the injection system clear. Fewer solids lead tominimized plugging of downstream equipment.

Different aspects, implementations and features are defined in detailherein. Each aspect, implementation or feature so defined may becombined with any other aspect(s), implementation(s) or feature(s)(preferred, advantageous or otherwise) unless clearly indicated to thecontrary.

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly indicates otherwise.

As used herein, the terms “comprising,” “including” and “having” areintended to be inclusive and mean that there may be additional elementsother than the listed elements.

In one implementation, the liquid hydrocarbon can comprise asphaltenecompounds. As used herein, “asphaltenes” are defined as the fractionseparated from crude oil or petroleum products upon addition of pentane.While difficult to characterize, asphaltenes are generally thought to behigh molecular weight, non-crystalline, polar compounds, which exist incrude oil. In one implementation, the liquid hydrocarbon can compriseasphaltene compounds in an amount of at least about three weightpercent, in the range of from about four to about 35 weight percent, orin the range of from five to 25 weight percent. Examples of asphalteniccrude oils include, but are not limited to, Merey heavy crude,Petrozuata heavy crude, Corocoro heavy crude, Albian heavy crude, BowRiver heavy crude, Maya heavy crude, and San Joaquin Valley heavy crude.

The flow of asphaltenic crude oils in pipelines can be improved by aDRA. In one implementation, the DRA is an ultrahigh molecular weightterpolymer having a glass transition temperature (T_(g)) of six degreesCelsius or below. The glass transition temperature of the ultrahighmolecular weight polymer is calculated using the Fox Equation:

$\frac{1}{T_{g}} = {\left( \frac{w_{1}}{T_{g\; 1}} \right) + \left( \frac{w_{2}}{T_{g\; 2}} \right) + {\ldots\mspace{14mu}\left( \frac{w_{x}}{T_{g\; x}} \right)}}$where w is the weight fraction of monomers 1 through x in the copolymer,and the numbered T_(g) values (Kelvin) are the glass transitiontemperatures for the homopolymers of the corresponding monomercomponents. In one implementation, the DRA is a terpolymer formed by afirst monomer, a second monomer, and a third monomer. The first, second,and third monomers correspond to different repeating units of theterpolymer. The first monomer is capable of forming a homopolymer havinga first glass transition temperature. The polymerization conditions forforming the homopolymer are the same as the polymerization conditionsfor forming the terpolymer. The second monomer is capable of forming ahomopolymer having a second glass transition temperature under the samepolymerization conditions as the terpolymer. In one implementation, thefirst glass transition temperature is at least 90 degrees Celsius higherthan the second glass transition temperature. For example, the firstglass transition temperature is about 90 degrees Celsius to about 180degrees Celsius higher than the second glass transition temperature. Inone implementation, the first glass transition temperature is at least120 degrees Celsius higher than the second glass transition temperature.For example, the first glass transition temperature is about 120 degreesCelsius to about 180 degrees Celsius higher than the second glasstransition temperature. In one implementation, the first glasstransition temperature is about 120 degrees Celsius to about 150 degreesCelsius higher than the second glass transition temperature. The thirdmonomer may be any suitable monomer, and the homopolymer formed with thethird monomer under the same polymerization conditions as the terpolymermay have a glass transition temperature in between those of the firstand second monomers. The first monomer imparts a high glass transitiontemperature to the terpolymer. It has been found that hard, brittlesolids formed during pumping of a conventional DRA including thehomopolymer or copolymer formed with the first monomer is the directresult of the higher glass transition temperature of the homopolymer orcopolymer, and the hard, brittle solids more readily block check valvesor other downstream equipment.

In order to reduce the amount of and to soften the hard, brittle solidswhile maintaining the amount of drag reduction in the asphaltenic crudeoils, the second monomer is included in the polymerization of theterpolymer. The second monomer is capable of forming a homopolymerhaving a glass transition temperature that is at least 120 degreesCelsius lower than that of a homopolymer that the first monomer iscapable of forming. The DRA comprised of the terpolymer formed with thesecond monomer produces softer solids and fewer solids due to the lowglass transition temperature of the terpolymer. The softer solids aremore easily handled by the pump to keep the injection system clear.Fewer solids lead to minimized plugging of downstream equipment. Thesecond monomer may be chemically similar to the third monomer, exceptthe second monomer is capable of forming a homopolymer having a glasstransition temperature that is lower than a homopolymer that the thirdmonomer is capable of forming. In some implementations, the secondmonomer, on its own, may negatively affect the amount of drag reductionin the asphaltenic crude oils. Thus, the DRA comprising the terpolymermay have a specific mole percentage of each monomer in order to maximizethe reduction and softening of the hard, brittle solids while minimizethe effect on the amount of drag reduction in the asphaltenic crudeoils. In one implementation, the terpolymer comprises five to 45 molepercent of the first monomer, 15 to 70 mole percent of the secondmonomer, and 10 to 80 mole percent of the third monomer. In anotherimplementation, the terpolymer comprises 10 to 40 mole percent of thefirst monomer, 20 to 60 mole percent of the second monomer, and 15 to 70mole percent of the third monomer. In another implementation, theterpolymer comprises 10 to 35 mole percent of the first monomer, 25 to50 mole percent of the second monomer, and 25 to 65 mole percent of thethird monomer.

The first monomer may include an aromatic ring, and examples of thefirst monomer include styrene, 4-methylstyrene, 4-(tert-butyl) styrene,benzyl methacrylate, and phenyl methacrylate. In one implementation, thefirst monomer is methyl methacrylate. In one implementation, the firstmonomer is styrene, and the styrene monomer is capable of formingpolystyrene having a first glass transition temperature of about 100degrees Celsius. The second monomer is 2-ethylhexyl acrylate, and the2-ethylhexyl acrylate monomer is capable of forming poly(2-ethylhexylacrylate) having a second glass transition temperature of about negative50 degrees Celsius. Thus, the first glass transition temperature isabout 150 degrees higher than the second glass transition temperature.The third monomer is 2-ethylhexyl methacrylate, and the 2-ethylhexylmethacrylate monomer is capable of forming poly(2-ethyhexylmethacrylate) having a third glass transition temperature of aboutnegative 10 degrees Celsius. The third monomer may be a general-purposebase monomer for constructing poly(meth)acrylate DRAs, such as2-ethylhexyl methacrylate. The second monomer, 2-ethylhexyl acrylate,may be chemically similar to the third monomer, and homopolymer of thesecond monomer has a glass transition temperature lower than that ofhomopolymer of the third monomer. Other suitable compounds for thesecond monomer may include n-butyl acrylate, benzyl acrylate, andisodecyl acrylate. In one implementation, the terpolymer comprises fiveto 45 mole percent of styrene, 15 to 70 mole percent of 2-ethylhexylacrylate or n-butyl acrylate, and 10 to 80 mole percent of 2-ethylhexylmethacrylate, and the terpolymer has a glass transition temperatureranging from about negative 38 degrees Celsius to about 6 degreesCelsius. In another implementation, the terpolymer comprises 10 to 35mole percent of styrene, 25 to 50 mole percent of 2-ethylhexyl acrylateor n-butyl acrylate, and 25 to 65 mole percent of 2-ethylhexylmethacrylate, and the terpolymer has a glass transition temperatureranging from about negative 28 degrees Celsius to about negative sixdegrees Celsius. With the terpolymer having a glass transitiontemperature of six degrees Celsius or below, fewer and softer solids areproduced when the terpolymer is used as a DRA.

The terpolymer used as a DRA may be dispersed in an aqueous continuousphase. The terpolymer can be prepared via emulsion polymerization of areaction mixture comprising monomers, a continuous phase, at least onesurfactant, and an initiation system. The continuous phase generallycomprises at least one component selected from the group consisting ofwater, polar organic liquids, and mixtures thereof. When water is theselected constituent of the continuous phase, the reaction mixture canalso comprise a buffer. Additionally, the continuous phase canoptionally comprise a hydrate inhibitor.

The surfactant used in the above-mentioned reaction mixture can includeat least one high HLB anionic or nonionic surfactant. The term “HLBnumber” refers to the hydrophile-lipophile balance of a surfactant in anemulsion. The HLB number is determined by the methods described by W. C.Griffin in J. Soc. Cosmet. Chem., 1, 311 (1949) and J. Soc. Cosmet.Chem., 5, 249 (1954), which are incorporated herein by reference. Asused herein, the term “high HLB” shall denote an HLB number of 7 ormore. The HLB number of surfactants for use with forming the reactionmixture can be at least about 8, at least about 10, or at least 12.

Exemplary high HLB anionic surfactants include, but are not limited to,high HLB alkyl sulfates, alkyl ether sulfates, dialkyl sulfosuccinates,alkyl phosphates, alkyl aryl sulfonates, and sarcosinates. Suitableexamples of commercially available high HLB anionic surfactants include,but are not limited to, sodium lauryl sulfate (available as RHODAPON LSBfrom Rhodia Incorporated, Cranbury, N.J.), dioctyl sodium sulfosuccinate(available as AEROSOL OT from Cytec Industries, Inc., West Paterson,N.J.), 2-ethylhexyl polyphosphate sodium salt (available from JarchemIndustries Inc., Newark, N.J.), sodium dodecylbenzene sulfonate(available as NORFOX 40 from Norman, Fox & Co., Vernon, Calif.), andsodium lauroyl sarcosinate available as HAMPOSYL L-30 from HampshireChemical Corp., Lexington, Mass.).

Exemplary high HLB nonionic surfactants include, but are not limited to,high HLB sorbitan esters, PEG fatty acid esters, ethoxylated glycerineesters, ethoxylated fatty amines, ethoxylated sorbitan esters, blockethylene oxide/propylene oxide surfactants, alcohol/fatty acid esters,ethoxylated alcohols, ethoxylated fatty acids, alkoxylated castor oils,glycerine esters, linear alcohol ethoxylates, and alkyl phenolethoxylates. Suitable examples of commercially available high HLBnonionic surfactants include, but are not limited to, nonylphenoxy andoctylphenoxy poly(ethyleneoxy)ethanols (available as the IGEPAL CA andCO series, respectively from Rhodia, Cranbury, N.J.), C8 to C18ethoxylated primary alcohols (such as RHODASURF LA-9 from Rhodia Inc.,Cranbury, N.J.), C11 to C15 secondary-alcohol ethoxylates (available asthe TERGITOL 15-S series, including 15-3-7, 15-S-9, 15-S-12, from DowChemical Company, Midland, Mich.), polyoxyethylene sorbitan fatty acidesters (available as the TWEEN series of surfactants from Uniquema,Wilmington, Del.), polyethylene oxide (25) oleyl ether (available asSIPONIC Y-500-70 from Americal Alcolac Chemical Co., Baltimore, Md.),alkylaryl polyether alcohols (available as the TRITON X series,including X-100, X-165, X-305, and X-405, from Dow Chemical Company,Midland, Mich.).

In one implementation, the initiation system for use in theabove-mentioned reaction mixture can be any suitable system forgenerating free radicals necessary to facilitate emulsionpolymerization. Possible initiators include, but are not limited to,persulfates (e.g., ammonium persulfate, sodium persulfate, potassiumpersulfate), peroxy persulfates, and peroxides (e.g., tert-butylhydroperoxide) used alone or in combination with one or more reducingcomponents and/or accelerators. Possible reducing components include,but are not limited to, bisulfites, metabisulfites, ascorbic acid,erythorbic acid, and sodium formaldehyde sulfoxylate. Possibleaccelerators include, but are not limited to, any composition containinga transition metal having two oxidation states such as, for example,ferrous sulfate and ferrous ammonium sulfate. Alternatively, knownthermal and radiation initiation techniques can be employed to generatethe free radicals. In another implementation, any polymerization andcorresponding initiation or catalytic methods known by those skilled inthe art may be used in the present invention. For example, whenpolymerization is performed by methods such as addition or condensationpolymerization, the polymerization can be initiated or catalyzed bymethods such as cationic, anionic, or coordination methods.

When water is used to form the above-mentioned reaction mixture, thewater can be purified water such as distilled or deionized water.However, the continuous phase of the emulsion can also comprise polarorganic liquids or aqueous solutions of polar organic liquids.

As previously noted, the reaction mixture optionally can include abuffer. The buffer can comprise any known buffer that is compatible withthe initiation system such as, for example, carbonate, phosphate, and/orborate buffers.

As previously noted, the reaction mixture optionally can include atleast one hydrate inhibitor. The hydrate inhibitor can be athermodynamic hydrate inhibitor such as, for example, an alcohol and/ora polyol. In one implementation, the hydrate inhibitor can comprise oneor more polyhydric alcohols and/or one or more ethers of polyhydricalcohols. Suitable polyhydric alcohols include, but are not limited to,monoethylene glycol, diethylene glycol, triethylene glycol,monopropylene glycol, and/or dipropylene glycol. Suitable ethers ofpolyhydric alcohols include, but are not limited to, ethylene glycolmonomethyl ether, diethylene glycol monomethyl ether, propylene glycolmonomethyl ether, and dipropylene glycol monomethyl ether.

In forming the reaction mixture, the monomers, water, the at least onesurfactant, and optionally the hydrate inhibitor, can be combined undera substantially oxygen-free atmosphere that is maintained at less thanabout 1,000 ppmw oxygen or less than about 100 ppmw oxygen. Theoxygen-free atmosphere can be maintained by continuously purging thereaction vessel with an inert gas such as nitrogen and/or argon. Thetemperature of the system can be kept at a level from the freezing pointof the continuous phase up to about 60 degrees Celsius, in the range offrom about 0 to about 45 degrees Celsius, or in the range of from 0 to30 degrees Celsius. The system pressure can be maintained in the rangeof from about 5 to about 100 psia, in the range of from about 10 toabout 25 psia, or about atmospheric pressure.

Next, a buffer can be added, if required, followed by addition of theinitiation system, either all at once or over time. The polymerizationreaction is carried out for a sufficient amount of time to achieve atleast about 90 percent conversion by weight of the monomers. Typically,this time period is in the range of from between about 1 to about 10hours, or in the range of from 3 to 5 hours. During polymerization, thereaction mixture can be continuously agitated.

In one implementation, the terpolymer has a weight average molecularweight (M_(w)) of at least about 1×10⁶ g/mol, at least about 2×10⁶g/mol, or at least 5×10⁶ g/mol. The continuous phase can have a pH inthe range of from about 4 to about 10, or in the range of from about 6to about 8, and contains few if any multi-valent cations. In oneimplementation, the terpolymer can comprise at least about 10,000, atleast about 25,000, or at least 50,000 repeating units selected from theresidues of the first, second and third monomers.

The terpolymer can be added to the liquid hydrocarbon, such as theasphaltenic crude oils, in an amount sufficient to yield a terpolymerconcentration in the range of from about 0.1 to about 500 ppmw, in therange of from about 0.5 to about 200 ppmw, in the range of from about 1to about 100 ppmw, or in the range of from 2 to 50 ppmw. In oneimplementation, at least about 50 weight percent, at least about 75weight percent, or at least 95 weight percent of the terpolymer can bedissolved by the liquid hydrocarbon. In another implementation, theviscosity of the liquid hydrocarbon treated with the terpolymer is notless than the viscosity of the liquid hydrocarbon prior to treatmentwith the terpolymer.

EXAMPLES

Chemicals: The monomers, 2-ethylhexyl methacrylate (Evonik),2-ethylhexyl acrylate (Sigma-Aldrich), and styrene (Lyondell), were usedwithout further purification. Sodium dodecyl sulfate (Polystep® B-5,Stepan Chemicals), ammonium persulfate (APS, Aldrich), iron (II) sulfateheptahydrate (Aldrich), ethylene glycol (Univar), Tergitol® 15-S-7(Dow), tert-butyl hydroperoxide (TBHP, Aldrich, 70%), sodium phosphatedibasic (Aldrich), and potassium phosphate monobasic (Aldrich) were allused without further purification. Type I water used in all experimentswas prepared using a Millipore water system.

Polymerization: Emulsion polymerizations were carried out under nitrogenin jacketed glass 300-mL or 1000-mL kettles. The experimental targetconditions were 40% polymer, approximately 5% total surfactant (1.2%Sodium dodecyl sulfate, 4% Tergitol® 15-S-7), and 5 degrees Celsiusstarting temperature. The redox initiator system was ammonium persulfateinitiator and iron (II) sulfate (FeSO₄) activator. All the ammoniumpersulfate was added at once, after which the FeSO₄ activator was addedas a solution using a syringe pump over an 18 hour period. The redoxchaser system utilized an “oil-soluble” initiator (TBHP) added all atonce followed by the activator (FeSO₄) added as a solution using asyringe pump over a two hour period. The total reaction time, initiationplus chaser plus hold time, was about 24 hours.

Example Polymerization: A 1000 mL jacketed reaction kettle with acondenser, mechanical stirrer, thermocouple, septum ports, and nitrogeninlet/outlet was set up. The kettle was charged with a buffer/surfactantsolution (465.20 g: sodium phosphate dibasic—0.184%; potassium phosphatemonobasic—0.177%; sodium dodecyl sulfate—2.13%; Tergitol® 15-S-7—7.08%;ethylene glycol—37.4%; water—balance) and purged with nitrogen for atleast one hour (0.4 lpm). Separately, the monomers were purged withnitrogen for at least one hour. The kettle was charged with 2-ethylhexylmethacrylate (185.22 g), 2-ethylhexyl acrylate (86.47 g), and styrene(48.59 g) by cannula using inert atmosphere techniques. Stirring wasinitiated at 450 rpm and the reactor cooled to about 5 degrees Celsiusby circulating fluid through the jacket. When the reaction mixturereached 5 degrees Celsius, APS solution (1.0 mL, 0.912 wt % APS) wasadded in one portion and stirred for a few minutes. Following this, iron(II) sulfate solution (5.0 mL, 0.245 wt % FeSO₄) was added to thereactor over an 18-hour period using a syringe pump. After completion ofthe initiation phase, the chaser phase commenced with the addition ofTBHP (1.0 mL, 0.367 wt % TBHP) added all at once and stirred for a fewminutes. This was followed by FeSO₄ solution (1.0 mL, 1.22 wt % FeSO₄)added over a two hour period using a syringe pump. At the end of thechaser addition, the polymerization was allowed to stir for a short timeand isolated.

While the foregoing is directed to implementations of the presentdisclosure, other and further implementations of the present disclosuremay be devised without departing from the basic scope thereof, and thescope thereof is determined by the claims that follow.

I claim:
 1. A drag reducing agent, comprising: a terpolymer comprising 5to 45 mole percent of a first monomer, 10 to 70 mole percent of a secondmonomer, and 10 to 80 mole percent of a third monomer, wherein the firstmonomer is styrene, the second monomer is 2-ethylhexyl acrylate, and thethird monomer is 2-ethylhexyl methacrylate.
 2. The drag reducing agentof claim 1, wherein the terpolymer has a glass transition temperature ofsix degrees Celsius or below.
 3. The drag reducing agent of claim 2,wherein the glass transition temperature of the terpolymer ranges fromabout negative 38 degrees Celsius to about six degrees Celsius.
 4. Thedrag reducing agent of claim 1, wherein the terpolymer comprises 10 to40 mole percent of styrene, 20 to 60 mole percent of 2-ethylhexylacrylate, and 15 to 70 mole percent of 2-ethylhexyl methacrylate.
 5. Thedrag reducing agent of claim 1, wherein the terpolymer comprises 10 to35 mole percent of styrene, 25 to 50 mole percent of 2-ethylhexylacrylate, and 25 to 65 mole percent of 2-ethylhexyl methacrylate.
 6. Thedrag reducing agent of claim 5, wherein the glass transition temperatureof the terpolymer ranges from about negative 28 degrees Celsius to aboutnegative six degrees Celsius.
 7. The drag reducing agent of claim 1,wherein the terpolymer has a weight average molecular weight of at leastabout 1×10⁶ g/mol.
 8. The drag reducing agent of claim 1, wherein theterpolymer has a weight average molecular weight of at least about 5×10⁶g/mol.
 9. The drag reducing agent of claim 1, wherein the terpolymercomprises about 50 mole percent of the 2-ethylhexyl methacrylate. 10.The drag reducing agent of claim 1, wherein the terpolymer comprisesabout 50 mole percent of 2-ethylhexyl methacrylate, about 25 molepercent of 2-ethylhexyl acrylate, and about 25 mole percent of styrene.11. The drag reducing agent of claim 1, wherein the drag reducing agentimproves the flow of crude oils having an asphaltene content of threepercent or higher.
 12. A drag reducing agent, comprising: a terpolymer,consisting essentially of: 10 to 35 mole percent of styrene; 25 to 50mole percent of 2-ethylhexyl acrylate; and 25 to 65 mole percent of2-ethylhexyl methacrylate.
 13. The drag reducing agent of claim 12,wherein the terpolymer has a glass transition temperature ranging fromabout −28 degrees Celsius to about −6 degrees Celsius.
 14. The dragreducing agent of claim 12, wherein the terpolymer has a weight averagemolecular weight of at least about 1×10⁶ g/mol.
 15. The drag reducingagent of claim 12, wherein the terpolymer has a weight average molecularweight of at least about 5×10⁶ g/mol.
 16. The drag reducing agent ofclaim 12, wherein the terpolymer consists of about 50 mole percent ofthe 2-ethylhexyl methacrylate.
 17. The drag reducing agent of claim 12,wherein the terpolymer comprises at least about 25,000 repeating unitsselected from the styrene, the 2-ethylhexyl acrylate, and the2-ethylhexyl methacrylate.
 18. A drag reducing agent, comprising: aterpolymer, comprising: about 50 mole percent of 2-ethylhexylmethacrylate; about 25 mole percent of 2-ethylhexyl acrylate; and about25 mole percent of styrene.
 19. The drag reducing agent of claim 18,wherein the terpolymer has a glass transition temperature ranging fromabout −28 degrees Celsius to about −6 degrees Celsius.
 20. The dragreducing agent of claim 18, wherein the terpolymer has a weight averagemolecular weight of at least about 1×10⁶ g/mol.